There exists a gaming machine that shows symbols with video reels and changes all the consecutive symbols on some of the video reels into WILDs when a predetermined condition is satisfied (for example, refer to US Patent Application Publication No. 2013/0310155). Each WILD substitutes for another kind of symbol to complete an advantageous winning pattern. Completion of a winning pattern leads to providing a predetermined payout or entering an advantageous game mode. For this reason, appearance of a WILD increases the player's expectation.
Furthermore, replacing all the consecutive symbols shown on some video reels with WILDs increases the probability of completion of multiple winning patterns; the player's expectation increases more.
This existing gaming machine displays the symbols by images; symbols can be changed easily by rewriting a specific storage area of the video RAM with the image data of WILD.